Optical fibers embedded in composite structural members hold promise for use as structural health monitoring sensors. Current technology employs a combination of an external light source, and an external demodulator, and a protective cable extension that is optically coupled to an optical fiber where the fiber exits the composite member. The external transmitters transmit electromagnetic radiation (hereinafter “light”) into the cables wherein the light encounters optical fiber sensors that cause sensible alterations to the transmitted light. The alterations may be linear (i.e. characterized by the same frequency of the transmitted light) or non-linear and are generally proportional, in some manner, to the condition the sensors are intended to measure. Thereafter, the altered light travels through the cables and reaches the external demodulators. The demodulator then converts (i.e. demodulates) the altered light to an electrical signal representative of the sensed condition.
Because the transmitters and demodulators discussed above are external to the composite members, the optical fiber must extend from the member, thereby presenting several problems. For instance, the external portion of the optical fibers are fragile and exposed to mechanical abuse. Thus, additional structural elements must be added to support and protect the external portion of the optical cables. Also, the egress of the cables from the composite members complicates the tooling (particularly the bonding jig) required for fabrication of the members. Further, during fabrication and assembly of the composite members into larger assemblies, the exposed optical cables necessitate careful handling. For these reasons a need exists to improve fiber optic structural health monitoring (“SHM”) systems.